In Situ Mixing in Microchannels

ABSTRACT

The present invention provides methods, systems and apparatus in which one fluid passes through an orifice or orifices and mixes with another fluid as it flows through a microchannel.

RELATED APPLICATIONS

This application is a divisional of Ser. No. 12/334,550 filed Dec. 15,2008, now U.S. Pat. No. 8,646,472, which was a divisional of Ser. No.10/848,559 filed May 17, 2004, now U.S. Pat. No. 7,470,408, whichclaimed priority to U.S. Provisional Application Nos. 60/531,006, filedDec. 18, 2003, which is incorporated herein as if reproduced in fullbelow.

FIELD OF THE INVENTION

This invention relates to mixing in microchannels.

INTRODUCTION

Mixing of one fluid into another is a process that is criticallyimportant to a wide variety of chemical processes. Because it is offundamental importance, great efforts have been made over many, manyyears to improve mixing quality and speed. For processes that requireexplosive combinations of reactants, safety is another, extremelyimportant consideration. One example of mixing two fluids can be foundin U.S. Pat. No. 6,471,937. In this patent, Anderson et al. describemixing a first reactant with a second reactant at a high velocity(preferably greater than 300 m/s) and short contact time (preferablyless than 0.5 milliseconds) before passing the mixture into a reactionchamber containing a solid catalyst. Anderson et al. provide examples ofmixing methane and oxygen. Although these examples permit estimation ofthe first reactant momentum flux, no details of the injection method(e.g., orifice number and size) are provided for the second reactant.Therefore momentum flux for the second reactant cannot be calculatedfrom these examples, and no optimal momentum flux ratio ranges for goodmixing can be inferred. In another example, Hamada et al. in U.S. Pat.No. 5,609,834 described mixing fuel into an oxidant through a porousplate and into a combustion chamber where the fuel and oxygen combust tocreate heat that is used to drive an endothermic reaction in an adjacentreaction chamber.

In recent years, reactors and other chemical processing apparatus havebeen designed with extremely small internal dimensions (that is,microchannel dimensions) in order to take advantage of the very shortmass transfer and heat transfer distances that are obtainable inmicrochannel apparatus. Another advantage of microchannels is that themicrochannel dimensions can be less than the quench diameter of anexplosive mixture and therefore can be substantially safer thanconventional apparatus. Some examples of mixing fluid streams inmicrochannel apparatus have been described by Tonkovich et al. in WO01/12312. In another example, see WO 02/064248 A2, Tonkovich et al.describe flowing reactants in separate parallel streams and combiningthese streams at a T-joint immediately before passing the combinedstream into the reaction chamber of a microchannel device.

Despite these and other efforts over many years, there remains a needfor faster and more efficient mixing techniques, and especially for newmixing techniques in microchannel apparatus.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a method of conducting areaction within a microchannel device, comprising: flowing a first fluidin a microchannel and flowing a second fluid through the at least oneorifice and into the microchannel that mixes with the first fluid. Themicrochannel comprises a solid catalyst disposed in at least one sectionof the microchannel. The microchannel is defined by a microchannel wallor walls and at least one orifice is present in the microchannel wall orwalls. The at least one orifice is disposed at a section of themicrochannel that does not contain catalyst.

The invention also provides a microchannel reaction system, comprising:a microchannel comprising a first reactant fluid; wherein themicrochannel comprises a solid catalyst disposed in at least one sectionof the microchannel; wherein the microchannel is defined by amicrochannel wall or walls and wherein at least one orifice is presentin the microchannel wall or walls; and wherein the at least one orificeis disposed at a mixing section of the microchannel that does notcontain catalyst, wherein a second reactant fluid flows through the atleast one orifice and wherein substantially no reaction occurs in themixing section.

In another aspect, the invention provides a method of conducting areaction using a microchannel device, comprising: flowing a firstreactant in a microchannel; wherein the microchannel is defined by amicrochannel wall or walls and wherein at least one orifice is presentin the microchannel wall or walls; wherein a first section of themicrochannel is defined by a first hydraulic diameter and a secondsection of the microchannel is defined by a second hydraulic diameterthat is larger than that of the first section; wherein the first sectionis disposed upstream of the second section; wherein the at least oneorifice is disposed upstream of the second section; and flowing a secondreactant through the at least one orifice and into the microchannel.

In a further aspect, the invention provides a method of mixing fluids ina microchannel, comprising: passing a first fluid through a microchannelthat has at least two orifices; and passing a second fluid through theat least two orifices. The second fluid flows into the first fluid at amomentum flux ratio in the range of 10 and 400, more preferably between40 and 200.

In another aspect, the invention provides a method of mixing fluids in amicrochannel, comprising: flowing a first fluid in a first directionthrough a microchannel and flowing a second fluid in a second directionthrough a first channel. The second direction is at an angle of 45° to135° relative to the first direction. The microchannel is defined by atleast one channel wall and the channel wall has at least one orifice. Aportion of the first channel is adjacent to the microchannel. At a pointwhere the first channel is adjacent to the microchannel, a portion ofthe second fluid flows through the at least one orifice and mixes withthe first fluid. A third fluid flows in a third direction through asecond channel. The third direction is at an angle of 45° to 135°relative to the first direction. A portion of the second channel isadjacent to the microchannel. In this aspect, “adjacent” means that thechannels share a common wall.

In another aspect, the invention provides microchannel apparatus,comprising: a microchannel having a central axis (defined by linethrough center of cross-sectional area) that extends in a firstdirection; a first channel having a central axis (defined by linethrough center of cross-sectional area) that extends in a seconddirection; wherein the second direction is at an angle of 45° to 135°relative to the first direction; wherein the microchannel is defined byat least one channel wall and the channel wall has at least one orifice;wherein a portion of the first channel is adjacent to the microchannel;wherein, at a point where the first channel is adjacent to themicrochannel, the at least one orifice connects the microchannel withthe first channel; and a second channel having a central axis (definedby line through center of cross-sectional area) that extends in a thirddirection; wherein the third direction is at an angle of 45° to 135°relative to the first direction; wherein a portion of the second channelis adjacent to the microchannel.

In a further aspect, the invention provides a system that mixes fluidsin a microchannel, comprising: a first fluid flowing in a microchannel;a second fluid flowing in a direction in a conduit that is adjacent tothe microchannel; wherein the second fluid is flowing into the conduitwith a momentum number of 0.05 or greater; wherein the second fluidflows into the first fluid in the microchannel through at least twoorifices that connect the conduit and microchannel; wherein the at leasttwo orifices comprise a first orifice and a second orifice and whereinthe second orifice is further in said direction than the first orifice;wherein the first orifice comprises a first cross-sectional area and thesecond orifice comprises a second cross-sectional area; and wherein thesecond cross-sectional area is smaller than the first cross-sectionalarea. In a preferred embodiment, the first cross-sectional area of thefirst orifice is adjacent to the conduit; the second cross-sectionalarea of the second orifice is adjacent to the conduit; the first orificecomprises a third cross-sectional area that is adjacent to themicrochannel; the second orifice comprises a fourth cross-sectional areathat is adjacent to the microchannel; and the third and fourthcross-sectional areas are substantially the same. In another preferredembodiment, the orifices are not tortuous (this is a preferredembodiment of all of the aspects described herein).

The ratio of the manifold's head to its friction loss, momentum number(Mo), is defined by the following equation:

${Mo} = {\frac{\frac{1}{2\rho}\left\lbrack {G^{2} - 0} \right\rbrack}{\frac{4{fL}}{D}\frac{G^{2}}{2\rho}} = \left\{ \frac{4\; {fL}}{D} \right\}^{- 1}}$

where,D [m]=manifold hydraulic diameter at the manifold reference pointf [dimensionless]=Fanning friction factor for the manifold referencepointL [m]=length of the manifoldG [kg/m²/s]=mass flux rate at the manifold reference pointρ [kg/m³]=Density of the fluidConsidering the case of a manifold having plural orifices (orifices areone type of connecting channel): the reference point of header manifoldReynolds number, mass flux rate, density and hydraulic diameter for themomentum number are defined at the position on the manifold channel axiswhere the wall plane closest to the header entrance belonging to theconnecting channel closest to the entrance in the manifold connects withthe manifold channel axis. In the typical, simple case, the length L isthe distance from the “first” orifice to the “last” orifice in a seriesof orifices that run down the length of a header (center line of thefirst orifice to center line of the last orifice). Generally, the lengthof the header manifold L is taken from the reference point to the end ofthe manifold, where the wall plane farthest away from the headerentrance belonging to the connecting channel farthest from the entrancein the manifold connects with the manifold channel axis. The equationsfor the footer manifold are analogous to the header manifold but thereference point is at the last orifice of the footer before the exit.The footer manifold Reynolds number, mass flux rate, density andhydraulic diameter for the momentum number are defined at a referencepoint at the position where the wall plane closest to the footer exitbelonging to the connecting channel closest to footer exit connects withthe manifold channel axis. The length of the footer manifold L is takenfrom the reference point to the beginning of the manifold, where thewall plane farthest away from the footer exit belonging to theconnecting channel farthest away from the footer exit in the manifoldconnects with the manifold channel axis.

In another aspect, the invention provides a method of mixing fluids in amicrochannel, comprising: flowing a first fluid in a microchannel;wherein the microchannel is defined by a microchannel wall or walls andwherein at least one orifice is present in the microchannel wall orwalls; wherein at the section of the microchannel comprising the atleast one orifice, the microchannel has a first hydraulic diameter;wherein the at least one orifice has a narrowest portion and thenarrowest portion has a second hydraulic diameter; and flowing a secondreactant through the at least one orifice and into the microchannel;wherein the ratio of the first hydraulic diameter to the secondhydraulic diameter is in the range of 2 to 6.

The invention further provides microchannel apparatus, comprising: amanifold adjacent to a microchannel along a plane; wherein themicrochannel is connected to the manifold via at least two orifices;wherein the manifold adjacent to a microchannel along a plane comprisesan open area having an outer perimeter; wherein said outer perimeter isdefined by the open area adjacent to the microchannel that is outside ofany orifices connected to the microchannel; and wherein the outerperimeter has a thickness that is at least 3 orifice diameters largerthan the diameter of the largest orifice that connects the manifold tothe microchannel.

In another aspect, the invention provides microchannel apparatus,comprising: a manifold adjacent to a microchannel; wherein themicrochannel is connected to the manifold via at least three orifices;wherein the at least three orifices are disposed about a plane ofsymmetry and wherein the at least three orifices are not in a straightline.

In a further aspect, the invention provides microchannel apparatus,comprising: a manifold adjacent to a microchannel; wherein themicrochannel is connected to the manifold via at least three orifices—acentral orifice and at least two orifices radially disposed from thecentral orifice; and wherein the at least two orifices have largercross-sections than the central orifice.

In yet another aspect, the invention provides a system in which at leasttwo fluids are mixed, comprising: a first fluid flowing through amicrochannel; and a second fluid flowing in a direction through aconduit that is adjacent to the microchannel. The microchannel isconnected to the conduit via at least two orifices. The orificescomprise shapes, viewed in the direction of flow through the conduit,that comprises a sequence of shapes selected from the group comprising:circular and triangular with one vertex pointed downstream; triangularwith one vertex pointed downstream and slot with the long axisperpendicular to flow direction; slot with the long axis parallel toflow direction and triangular with one vertex pointed downstream; andslot with the long axis parallel to flow direction and circular.

In a further aspect, the invention provides a system in which at leasttwo fluids are mixed, comprising: a first fluid flowing through amicrochannel; and a second fluid flowing in a direction through aconduit that is adjacent to the microchannel. In this aspect, themicrochannel and the conduit are separated by a microchannel wall andthe microchannel is connected to the conduit via at least onenon-circular orifice through the microchannel wall. Furthermore, the atleast one non-circular orifice comprises at least one straight segmenton the periphery of the orifice. In this aspect, there is not an orificeopposite the at least one non-circular orifice having at least onestraight segment on the periphery of the orifice. The microchannel has asecond microchannel wall that is opposite the wall comprising at leastone non-circular orifice having at least one straight segment on theperiphery of the orifice. The second fluid flows through the at leastone non-circular orifice having at least one straight segment on theperiphery of the orifice into the first fluid. In some preferredembodiments, heat is transferred through the second microchannel wall.

The present invention includes any of the designs described herein,including reactor designs and orifice designs, and any combination ofthe designs. However, the designs illustrated in the figures are merelyexemplary and are not intended to limit the invention. It should beappreciated that the invention includes any of the apparatus describedherein described in terms of microchannel chemical systems including theapparatus with fluids flowing through the apparatus. The invention canalso be described by the various parameters and values described in thedescriptions and examples.

Advantages

In many of the preferred embodiments, fluids are mixed in a zone thatdoes not contain any catalyst. There are several strong advantages formixing inside of microchannels, and away from a microchannelheterogeneous catalyst zone, including the following: safe mixing ofreactants within the flammability regime before the reaction zone;mixing of a diluent after the reaction section to quench a reaction orto move the mixture composition outside of the flammability regionbefore entering macro connections; avoiding damage to a solid catalyst;or avoiding unwanted entrainment of solid catalyst.

GLOSSARY

A “diluent” is a nonreactive fluid, inhibitor, or a safening agent (forexample, an agent that reduces flammability of a mixture).

In the present invention, a “microchannel” is defined as a channelhaving at least one dimension of 2 millimeters or less, in someembodiments 1 millimeters or less, and in some embodiments, 0.1 to 1millimeters. As is understood in the art, a microchannel is not merelyan orifice. The length of a microchannel (that is, the direction of flowduring normal operation) is not the shortest dimension of amicrochannel. Both height and width of a microchannel are substantiallyperpendicular to the direction of flow of reactants through the reactor.Microchannels are also defined by the presence of at least one inletthat is distinct from at least one outlet—microchannels are not merelychannels through zeolites or mesoporous materials. The height and/orwidth of a microchannel is preferably about 2 mm or less, and morepreferably 1 mm or less. Preferably, the length of a microchannel isgreater than 1 cm, in some embodiments in the range of about 1 to 50 cm.The sides of the microchannel are defined by a microchannel wall ofwalls. The choice of material for the walls depends on the intended use.These walls are preferably made of a hard material such as a ceramic, aniron based alloy such as steel, or monel. In some embodiments, themicrochannel walls are comprised of a stainless steel or Inconel® whichis durable and has good thermal conductivity. The microchannel devicescan be made by known methods, and in some preferred embodiments are madeby laminating interleaved plates (also known as “shims”), and in somepreferred embodiments, shims designed for reaction channels areinterleaved with shims designed for heat exchange.

In some preferred embodiments, the microchannel devices are microchannelreactors that include a plurality of microchannel reaction channels,preferably in thermal contact with a plurality of adjacent heat exchangemicrochannels. A plurality of microchannels may contain, for example, 2,10, 100, 1000 or more channels. In preferred embodiments, themicrochannels are arranged in parallel arrays of planar microchannels,for example, at least 3 arrays of planar microchannels. In somepreferred embodiments, multiple microchannel inlets are connected to acommon header and/or multiple microchannel outlets are connected to acommon footer. During operation, the heat exchange microchannels (ifpresent) contain flowing heating and/or cooling fluids. Non-limitingexamples of this type of known reactor usable in the present inventioninclude those of the microcomponent sheet architecture variety (forexample, a laminate with microchannels) exemplified in U.S. Pat. Nos.6,200,536 and 6,219,973 (both of which are hereby incorporated byreference). Performance advantages in the use of this type ofarchitecture include their relatively large heat and mass transferrates, and the substantial absence of any explosive limits. Microchannelreactors can combine the benefits of good heat and mass transfer,excellent control of temperature, residence time and minimization ofby-products. Pressure drops can be low, allowing high throughput.Furthermore, use of microchannel reactors can achieve better temperaturecontrol, and maintain a relatively more isothermal profile, compared toconventional systems. In addition to the process microchannel(s),additional features such as microchannel or non-microchannel heatexchangers may be present. Microchannel heat exchangers are preferred.Heat exchange fluids may flow through adjacent heat transfermicrochannels, and can be gases or liquids and may include steam, liquidmetals, or any other known heat exchange fluids—the system can beoptimized to have a phase change in the heat exchanger. In somepreferred embodiments, multiple heat exchange layers are interleavedwith multiple reaction microchannels (for example, at least 10 heatexchangers interleaved with at least 10 process microchannels.Microchannels are defined by microchannel walls that limit flow.

An “orifice” is a hole through a microchannel wall. Its length is thesame as the thickness of the microchannel wall (unless it is slanted inwhich case its length will be slightly greater than this thickness. An“orifice” is not a T-joint or “Y” joint; in other words, two channelsthat flow together to form a single channel (in the shape of a “T” or a“Y”) are not an orifice. In general, the mixing lengths of a T orY-joint are considerably longer than those created by orifices in thedescribed invention. The lengths may be two times, five times, or even10 times longer. The longer lengths create more time with a less wellmixed feed stream; the results of more time with a lower mixing qualitymay be a lower selectivity to the desired product, a larger device, orincreased safety concerns from a potentially flammable mixture.

“Opposing orifices” are orifices at opposite sides of a microchannelthat may or may not be identical in size and geometry and are alignedsuch that flow through the opposing orifices collide with each otherinside the microchannel.

A “reaction chamber” is a portion of a microchannel that contains asolid catalyst.

A “reaction zone” is a portion of a microchannel in which a reactionoccurs; this zone may contain a solid catalyst (in which case it is areaction chamber), or a solid catalyst may be absent but design features(such as an expanded diameter) can allow a reaction to proceed.

A detonation cells size is an empirically-determined value measured whena gas-phase detonation is propagated down a tube or channel. A smokedfoil inner lining records the shock wave patterns as the detonation waveproceeds through an experimental device. The passage of the detonationwave leaves a characteristic “fish-scale” pattern etched on the smokedfoil, each of which is called a detonation cell. The distance from thebeginning to the end of a single detonation cell in the axial directionof the tube or channel is termed the detonation cell size, λ. Empiricalstudies using detonation of hydrogen and other hydrocarbon compounds inthe presence of oxidants indicate the minimum gap for high aspect ratiochannels to support detonation transmission is at least as large as thecomposition detonation cell size. This guidance holds for channels ofall aspect ratio. A general discussion of the concept of detonation cellsize and how it can be determined is described in the followingreferences:

-   Glassman, I., 1996, Combustion, Academic Press, 252-259.-   Moen, I. O., 1993, “Transition to detonation in fuel-air explosive    clouds,” Journal of Hazardous Materials, 33, 159-192.-   Berman, M., 1986, “A Critical Review of Recent Large-Scale    Experiments on Hydrogen-Air Detonations,” Nuclear Science and    Engineering, 93, 321-347.

For purposes of the present invention, a “system” is a combination ofapparatus and fluids in the apparatus. In some preferred embodiments, asystem further includes properties such as pressure and flow rates.

As is accepted, conventional terminology, “tangent-to-tangent” distanceis the distance between the closest edges of two orifices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 schematically illustrate shim designs for combiningfluids.

FIG. 3A-3E illustrates various examples of orifice configurations.

FIG. 4 schematically illustrates a microchannel reactor with stagingbetween catalyst zones.

FIG. 5 schematically illustrates a porous structure in a mixing zone.

FIG. 6 schematically illustrates a system with opposing orifices twocombine two fluids and a third fluid added after a catalyst zone.

FIGS. 7-9 schematically illustrate reduced diameter zones inmicrochannel apparatus.

FIGS. 10 a-10 c schematically illustrate microchannel apparatus withcoplanar, adjacent channels for heat exchange and fluid distribution.

FIG. 11 schematically illustrates partial channels in a manifold region(footer or header).

FIG. 12 schematically illustrates a design for equalizing flow throughorifices.

FIG. 13 is a cut-away view of a device tested for adding gas into amanifold and through holes to mix in a microchannel.

FIG. 14 is an alternate view of the device of FIG. 13.

FIG. 15 is a design showing a preferred separation between the outer setof orifices and outer perimeter wall of the orifice manifold viewed inthe plane of the injection orifices.

FIG. 16 illustrates an example of a preferred orifice configuration withsquare pitch repeating unit rotated 45 degrees relative to flowdirection and plane of symmetry indicated.

FIG. 17 illustrates an example of a preferred orifice configuration forradial distribution.

FIG. 18 illustrates various orifice jet plume shapes and orientationfollowing injection into a mixing channel containing a cross-flowingfluid stream.

FIG. 19 shows the jet orifice configuration for the 0.500-Inch WideMixing Channel with a 0.040-Inch Flow Gap of the examples and FIG. 13.All dimensions are in inches. The + marks indicate circular orificeshaving a diameter of 0.017 inch.

FIG. 20 is a view of the apparatus of the examples showing the lengthsused for the calculations in Table 3.

DETAILED DESCRIPTION OF THE INVENTION Mixing Prior to a Reaction Zone

The mixing of reactants, such as oxidants and hydrocarbons, may occurupstream of a reaction chamber, preferably within a microchannel eitherimmediately upstream from the catalyst zone or further upstream andseparated by a heat exchange section or by another section forconducting a first reaction or a separation. It may be advantageous tomix streams, such as methane and oxygen, immediately after entering adevice at low temperature. The combined flammable mixture may then flowthrough an integral heat exchanger to raise the mixture temperatureprior to entering a catalytic zone housed within the contiguousmicrochannel.

In some embodiments, otherwise explosive mixtures can be safely handledinside microchannels due to quenching at the microchannel walls thatprevents explosions or thermal runaway. The mixture may undergoadditional heat exchange to raise or cool the temperature as desired.The mixture also may not undergo additional heat exchange. The resultingflammable mixture, that was formed within the microchannel, may thenflow directly into a minichannel (dimensions above the critical quenchdiameter for the fluid mixture) where a desired homogeneous combustionreaction may occur. This can, for example, generate heat or power, orreduce emissions. A homogenous combustion reaction can be safely sparkedor ignited within the minichannel with the use of embedded resistiveelements (and other methods). The volume of each parallel minichannel issufficiently small with enough surrounding metal that detonation can notoccur while the homogenous combustion reaction may occur. In preferredembodiments, each dimension of a minichannel exceeds 2 millimeters. Insome preferred embodiments, each dimension of a minichannel exceeds 2 mmand is no larger than 20 mm. The minimum minichannel dimension for safeoperation is a function of the composition of the flammable mixture,along with the temperature and pressure. The hot gas exiting acombustion minichannel may then be further diluted with a quench streamor it may alternatively undergo rapid heat removal to add heat to anadjacent stream while also advantageously stopping the NOx formationreactions. Very low NOx is envisioned because the reactants will spendless time at the high combustion temperatures before being rapidlyquenched with fast cooling (exceeding 100 degrees per second).

Mixing of a Diluent after the Reaction Zone

A distinct fluid stream may be mixed with a product stream exiting areaction zone. In this manner, the product mixture may be diluted tomodify the composition outside of the flammable region or to addmolecules (such as steam for some reactions) that directly inhibitcontinued undesired reactions. In many situations, it may be desirableto prevent further reactions, for example reactions catalyzed byinteractions with the channel walls, non-selective homogeneous reactionscaused by free radials generated in the catalyst containing section orelsewhere, or the formation of coke or carbon or polymerization ofproducts (acrylonitrile etc.). This can be done in situ in amicrochannel by the introduction of a quenching or safening agent (forexample, steam, nitrogen, methane, hydroquinone etc.) into the stream ata location downstream from where the catalyst is disposed (see additionof fluid C in FIG. 6).

Diluent may be added immediately downstream of the reaction zone or maybe added some distance away from the reaction zone. As an example forthis latter case, a flammable mixture may exit the reaction zone of themicrochannel, flow through an integral exchanger section in a connectingmicrochannel to remove heat, and then undergo mixing with a diluent tomove the mixture composition outside of the flammable region prior toexiting the microchannel and enter large connecting macro pipes, ducts,and the like.

The addition of a diluent prior to exiting the microchannel may be partof a plant control scheme. As an example, if the conversion is low inthe reaction zone such that sufficient oxygen remains to make theproduct mixture flammable, more diluent could be added to the productstream flowing within the microchannel before it exits the device.Further, a feed-back control loop could be employed where the measuredreaction temperature or product mixture controls how much diluent issafely added to the flammable mixture in the microchannel before itexits and flows to conventional hardware. In this case, catalystpoisoning or deactivation or process upsets do not create a furtherdownstream safety issue.

An advantage of adding the diluent near the end of the microchannel isthat the diluent stream would not be required to undergo heat exchangeto heat near the reaction temperature and then cool down to the exittemperature. This reduces lost work from entropic losses in recuperatingenergy from a stream that is heated and then cooled for the purpose ofonly conducting a mixing unit operation at elevated temperature.

Mixing in a Manifold

Mixing can occur in manifolds (which may or may not have a dimension of2 mm or less), and this mixing may occur separately or in conjunctionwith mixing in one or microchannels to which the manifold is connected.Manifold structures are described in detail in U.S. Pat. No. 7,422,910filed Oct. 27, 2003, which is incorporated herein as if reproduced infull below (see especially FIG. 28 and the corresponding description).The present invention includes methods in which fluid streams are mixedthrough orifices that form passages to a manifold.

For example, the addition of a diluent could be incorporated within amanifold section or other region of a microchannel device such that aminimal amount of extra device volume is required to embed this safetyfeature within the design. An example is schematically illustrated inFIG. 11. Partial channels are added in the manifold region to add afluid into a footer and/or header. The fluid could be any of the fluidsdiscussed here such as a reactant or diluent. In a preferred embodiment,diluent 1 or diluent 2 or optionally both diluents are is added tosafely mix flammable mixtures or dilute flammable mixtures before theyleave a microchannel and enter macro fluid connections.

Reaction Classes

Generally, the present invention relates to any process (or system orapparatus) that mixes (or is capable of mixing) at least two fluidswithin a microchannel. In some preferred embodiments, the process is achemical reaction. The following is a non-limiting list of reactions inwhich micromixing can be employed: alkylation (liquid phase, gas phase);nitration (gas phase); oxidation (liquid Phase, gas Phase);hydrogenation/hydrocracking (liquid phase, gas phase); lithiation(liquid phase); catalytic cracking (solid/gas or 3 phase); epoxidation;and polymerization.

Designs for Mixing in Microchannels

Methods of constructing microchannel apparatus are well-known and neednot be described here. Making microchannel devices by stacking sheets ofmaterials having channels and other components cut partially or fullythrough the sheets is the preferred technique for making apparatus ofthe types described.

General Classes and Layout

In Situ mixing of two or more streams, be they reacting or non-reactingor combinations thereof, can be accomplished in a variety of waysdepending upon the intent of the design. Examples of mixing schemesinclude:

-   -   Class 1: Designs in which the fluids to be mixed flow in        alternating parallel plane (see FIG. 1);    -   Class 2: Designs in which the fluids to be mixed flow in the        same plane (see FIG. 2);    -   Class 3: Designs in which the fluids to be mixed flow in the        same plane and in alternating parallel planes.

A basic Class 1 design layout can be seen in FIG. 1 in which twospecies, A & B, are to be mixed. Fluid A flows in a microchannel inwhich a catalyst is disposed. The catalyst can be of any conceivableform such as a powder, felt, fiber, foam, fin, wad, screen mesh, gauze,wall coating, or other structure. Fluid B flows in a channel that liesin a plane parallel to that in which fluid A flows. At a point prior tothe point at which the catalyst is disposed in the channel fluid B isintroduced into fluid A. This may be accomplished as shown in FIGS. 1and 2 in which fluid B is introduced into fluid A from opposite sides ofthe channel using orifices such as circles, slots, triangles, squares,rectangles or other geometrical figures as may be appropriate for thedesired mixing effect. Introduction of fluid B into fluid a may also beconducted from only one side of the channel (remove one of the orificesin FIG. 1 or 2) or, in the case of Class 3 type designs fluid B may beintroduced into fluid A from three or more sides of the channel. Iforifices are disposed on both sides of the channel as in FIGS. 1 and 2,the orifices need not be opposed but may be offset from one another orlaid out in any way found to be appropriate. Although FIGS. 1 and 2 show90° inlet angles, orifice walls can be sloped so that streams are mixedinto each other at an angle other than 90°. In some embodiments, twoorifices located in the same plain (on the same side) may be locatedsuch that the flow of one jet interacts with the flow fields produced bythe other in a manner that enhances mixing. For simplicity ofrepresentation, only one orifice is shown per side in FIGS. 1 and 2.However, any number of orifices (for example, at least 2, or at least 5orifices in one plate that connect a single microchannel with a sourceof another fluid—preferably this source is another microchannel) may beemployed as appropriate to the specific situation. All of thesubsequently described geometries are shown in the figures as Class 1,but it should be clear to anyone skilled in the art that they could beexecuted as Class 2 or Class 3 type schemes. In addition, figures areshown for the mixing of two fluids, A & B, but this could be extended toany number of different fluids both reacting and non-reacting.

Inter Bed In Situ Mixing

One application for in situ type mixing operation is the staging ofreactant between catalyst zones (see FIG. 4). In this example, it may bedesirable to introduce one or more streams into a flowing process streamat several axial locations along the microchannel that do not containcatalyst. This layout would be desirable, for example, in cases wherethe catalyst is very sensitive to one of the reactants and where highpartial pressures of species B could lead to side reactions. This modemaintains a low overall partial pressure of species B and at the sametime reduces the possibility that the catalyst will be exposed to highconcentrations of B. In a second embodiment, different catalysts couldbe disposed along the channel such that ethane could be mixed withoxygen converted to ethylene and the product mixture again mixed withoxygen and allowed to pass over a catalyst to produce acetic acid. Eachintroduction need not be the same and different species ratios could betailored to the suit desired reaction conditions. A third embodiment hasdifferent catalysts disposed along the channel and the secondintroduction of B could be replaced by third species. The number ofspecies, catalysts and conditions and chemical transformations can beextended to any desired degree.

Structures within Mixing Zones

In many preferred embodiments of the present invention, a mixing zonedoes not contain a catalyst; however, various noncatalytic structurescan be employed in the mixing zones. For example, a stream comprisingtwo fluids can flow into and contact each other in a porous structure(see FIG. 5). This structure can be of regular proportions (such as ahoneycomb cell structure) or be of random structure and could becomprised of powder, foam, felt (nonwoven), mesh or other material. Thestructure can have non-interconnected channels (such as a honeycomb) orinterconnected (such as a foam). This layout would be suitable forsituations in which A and B (or combination of any number ofconstituents) is highly reactive at the concentration levels that mayexist while mixing is underway but that are not once the mixture is ofuniform concentration (e.g., outside of flammability limits). Byintroducing the species in a structure with small critical diameterdetonation and deflagration can be suppressed until the mixture is ofuniform composition. In cases in which the final mixture is alsopotentially explosive or flammable the porous structure can be extendedto and contact the catalyst (fin, foam, powder or other material withsmall diameter pores).

In Situ Mixing in Reduced Gap Zones

In cases where it is not possible to employ a porous contactingstructure (FIG. 5) or where the quench diameter or detonation cell sizeis large enough it may be desirable to introduce a reactant into a fluidstream in a section of channel that contains a reduced gap. This couldbe accomplished by reducing the channel gap in the section containingthe orifices as depicted in FIGS. 7 through 9.

Coplanar, Adjacent Channels for Heat Exchange and Fluid Distribution

Another means of distributing and mixing of a second fluid into a firstfluid flowing in a microchannel is shown in FIG. 10. The fluiddistribution plenum is directly above the mixing zone in an adjacentplane. The plenum's axis is perpendicular to the axes of the unitoperation microchannel array. The distribution plenum's flow comes fromthe side and the distribution connections to the unit operationmicrochannel array are used to meter the correct amount of flow to eachchannel. The metering can be passive or active, passive control can beobtained, for example, by controlling channel dimensions. Thedistribution connections can be part of the fluid distribution plenum,the wall separating two streams and the unit operation microchannel, ora combination of all or some of these channels. A fluid plenum flow thatis perpendicular to the flow of the microchannels, provides room in thesame plane for other unit operations such as heat removal. The sectionof the microchannel to which the distribution plenum delivers fluid is amixing zone. This zone can be open to flow or may contain a static mixeror mixers, such as a porous material. In some embodiments, an orificeconnects the mixing zone to a reactor zone that contains a solidcatalyst. The fluid distribution plenum is separated from the other unitoperations by a dividing wall that maintains a hermetic seal from thetwo zones. This allows the device to distribute fluid flow outside theplane stacking envelope, as pictured in FIG. 10. FIG. 10 shows the areain the fluid distribution plane separated from a heat exchange surfaceused to cool the reactor section.

In the particular embodiment illustrated in FIG. 10 a, a process fluid101 flows in the plane of the page in channel 103. The channel containscatalysts 105, 107. A second fluid passes through perpendicular channels109, 111 and a portion of the secondary fluid flow passes throughorifices 113 and combines with fluid 101 in mixing area 115. A set ofsecondary channels 117, 118, 119, 120, which run parallel to channels109, 111 may carry a heat exchange fluid to add or remove heat to/fromthe process channel (in some preferred embodiments heat exchange regionsare matched to catalyst-containing regions). The pattern of channels canbe repeated to any desired extent; for example, at least 3 processchannel layers separated by intervening layers each of which containsecondary fluid and heat exchange fluid channels. If multiple secondaryfluid channels are present, they may contain different compositions; forexample lower concentrations of a reactant along the length of theprocess channel. A segment of a layer with a secondary and heat exchangechannel is illustrated in FIG. 10 b. In the illustrated embodiment, theheat exchange channel contains manifolding for more equal flowdistribution across the channel. Flow of the heat exchange fluid (i.e.,net flow) is substantially perpendicular to the first process fluid andcounter to the secondary fluid. The secondary fluid is distributed intoseveral process channels through orifices 113. Although the illustratedprocess channels and secondary channels are perpendicular; it should beappreciated that other orientations are possible (although moredifficult to construct).

Orifice Designs

Streams may be mixed together within a microchannel through the use oforifices or openings, such as circular, triangular, and slot jets. As isconventionally understood, an orifice is a hole through a microchannelwall; a hole is not a T-joint. Flow through these orifices is typicallyhigh, exceeding 1 m/s and in some embodiments greater than 10 m/s, andin other embodiments exceeding 50 m/s. Mixing may also be enabled byfeeding a reactant through a porous plate or wall that separates twofluids. One example is the use of a sintered metal plate that maintainssmall average pore sizes. One such porous sintered metal plate may beobtained from MOTT and may have an average pore size ranging from 0.01micron to 100 microns. A typical range of average pore size is from 0.1micron to 10 microns. Preferably, however, the orifices are not pores ina porous plate having randomly distributed and tortuous porosity;instead, specifically designed configurations (such as may be formed bydrilling) are preferred.

Generally, the spatial distribution of jets or the jet orifice patternshould take advantage of some degree of symmetry to effectively causemixing across the entire cross-section of the flow channel. Inrectangular micro channels, two types of jet distributions are believedto be highly effective for mixing: (1) triangular pitch jets and (2)rectangular pitch jets. In the case of triangular pitch jets, if jets oftwo unequal hydraulic diameters are used, the pattern generalizes toisosceles pitch with only two sides of the pitch of equal size asdepicted in FIG. 3A. When all jet orifices are identical, the pitchreduces to an equilateral triangle design as in FIG. 3B. For arectangular pitch design, if jets of unequal hydraulic diameter areused, the pattern generalizes to rectangular pitch with only two sidesequal as illustrated in FIG. 3C. Should the jet orifices themselves beidentical, this pattern reduces to a square pitch design as given inFIG. 3D. Finally, there are “degenerate” cases and hybrid combinationsof both basic patterns as illustrated in FIG. 3E.

Another consideration when designing systems that mix a fluid or fluidsinto microchannels is momentum effects within a channel carrying asecond fluid (that is, a fluid that is to be injected). In this regard,a channel or other conduit carrying the second fluid can be treated as amanifold using the design considerations described at length inincorporated U.S. Pat. No. 7,422,910 filed Oct. 27, 2003. If the designemploys a large pressure drop between the conduit carrying a secondfluid and the microchannel carrying the first fluid (where the conduitand the microchannel are connected via orifices), then the orifices canhave the same geometry. On the other hand, for high momentum flows,where the momentum number is 0.05 or greater, it is useful to have theorifices constricted in the direction of flow such that the increases instatic pressure in the manifold from momentum compensation, generated byturning the manifold flow into the orifices, can be managed byincreasing the turning losses into the orifices to achieve the desiredpressure profile in the orifices. This decreases the cross-sectionalarea for flow into the connection and increases the turning loss fromthe delivery manifold to the connection. More preferably, the orificesinclude two cross-sectional areas, a first cross-sectional area thatdecreases in the direction of flow, and a second cross-sectional areathat is substantially the same in each of the orifices. This isillustrated in FIG. 12. In some embodiments, it is preferred that fluidmomentum out of the connection should be substantially similar fromconnection to connection in a given delivery manifold. This means theconnection's shape and cross-sectional area need to be substantiallysimilar for each connection for a given delivery manifold as isillustrated in FIG. 12. A nominal length (can be as small asmanufacturable) C₁ is needed for a sudden cross-section change toaccelerate (or decelerate) the flow in a second section of theconnection. The first section of the connection can have a differentcross-sectional area and shape than the second section. It should beappreciated that these manifolding considerations can be combined withthe other orifice considerations to make more complex patterns in whichmore complex orifice configurations are repeated down the length of aconduit with decreasing cross-sections to adjust for momentum.

If the pressure drop into the connecting channels is low (less than1.4×10⁴ Pa) and the momentum number is lower than 0.05, the frictionlosses drive flow distribution more and the static pressure decreases inthe direction of delivery manifold flow due to continuous frictionlosses. Thus the cross-sectional area of the connection's first sections(C₂) should increase in the direction of delivery manifold flow to lowerthe turning and frictional losses for the flow entering the connection.This decrease in connection flow resistance then offsets the decrease instatic pressure in the delivery manifold Orifice mixing performance canbe related to the momentum flux ratio and in turn to the ratios of thehydraulic diameters of the channel to the hydraulic diameter of theorifice. Based upon numerous computational fluid dynamic simulations oforifice mixing, the preferred range of ratio of mixing channel hydraulicdiameter to orifice hydraulic diameter is 2 to 15, more preferablybetween 2.5 and 4.5, and most preferably between 3.3 and 4.5. Theseranges apply to both opposing and non-opposing jets, however the orificegeometry and number of orifices may differ depending upon whether anopposing or non-opposing application is used. In preferred embodiments,each mixing section includes at least 3 opposing orifices and morepreferably 5 or more opposing orifices.

It is desired to have a low pressure drop through the orifices into aprocess microchannel. Preferably this pressure drop is 2 pounds persquare inch (psi) (1.4×10⁴ Pa) or less, more preferably 1 psi (0.7×10⁴Pa) or less, and still more preferably 0.5 psi (3.4×10³ Pa) or less.

Generally when designing a micro-mix orifice configuration, there areseveral best practices to be followed for achieving good mixing for aminimal distance downstream of the orifice region.

-   -   1. Injection Stream Plenum Size. The plenum dimensions as given        by (127) and (128) in FIG. 13 of the example should be sized        appropriately to achieve good flow distribution into the        individual injection orifices. Specifically, the outer perimeter        of the manifold in the plane of the stream injection orifices        should exceed the outer set of jets by at least 3 orifice        diameters (dimension D in FIG. 15) and more preferably 5 orifice        diameters and most preferably 10 orifice diameters. Secondly,        the ratio of plenum height (128) to width (127) should be at        least 1:10 and more preferably 1:3 and most preferably 1:1.    -   2. The fluid injection orifices should be geometrically        configured so that one upstream orifice does not occlude flow        and prevent good mixing for a downstream orifice. Such        configurations use a repeatable pattern of orifice sizes and        locations where the repetition pattern comprises at least one        plane of symmetry. An example of such a preferred configuration        is given in FIG. 16. Preferred configurations include triangular        pitch arrays, square pitch arrays when the lines representing        the sides of the squares are oriented at an angle of 45 degrees        to the direction of bulk stream channel flow, and radial        distribution from a center orifice. If an orifice distribution        radiating away from a central axis is used, it is preferred that        a graded orifice size away from the central axis be used, with        the orifices either increasing or decreasing in area as a        function of distance from the center axis. A preferred example        of radial distribution that uses a center orifice that is        largest and each successive set of orifice as one proceeds from        the center orifice becomes gradually smaller is illustrated in        FIG. 17.    -   3. If only one type of orifice geometry is used, then it is        preferable if they are all circular to promote inter-stream        diffusion and good mixing. Slot orifices, triangular orifices,        and other non-circular shape orifices can also be used but        should be used in a particular combination to promote good        mixing. The preferred combinations are given in Table 1. The        invention includes orifice constructions that include these        configurations, preferably in immediate order (i.e., with no        intervening orifices.

TABLE 1 Preferred Configuration for Ordering of Non-Circular andCircular Orifices. Upstream Orifice Downstream Orifice Circular Trianglewith one vertex pointed downstream Triangular with one vertex Slot withlong axis perpendicular to flow pointed downstream direction Slot withlong axis Triangle with one vertex pointed upstream perpendicular tobulk flow direction Triangle with one vertex Slot with long axis pointedparallel to flow pointed upstream direction Slot with long axis pointedCircular parallel to flow direction Notes (1) The ordering is based onnearest neighbor orifices in the flow direction, (2) flow directionrefers to bulk channel flow in the mixing zone, (3) upstream means inthe direction counter to the bulk channel flow direction from thereferenced orifice, (4) downstream means in the same direction as thebulk channel flow direction from the referenced orifice.

The selection of orifice shape is primarily driven by the decision ofwhether to use an opposing or non-opposing orifice design. Non-circularorifices provide the most benefit to mixing enhancement when they areused in a non-opposing application. The fluid injected by a circularorifice into a cross-flow channel stream generally diffuses moreefficiently. This in turn results in a more dispersed jet plume and themomentum flux dissipates more rapidly than for non-circular plumes asthe flow passes through the channel. This phenomena results from thefact that the circular orifice has everywhere the same radius ofcurvature as one proceeds around its perimeter. Noncircular orificesperform differently from a mixing standpoint because the radius ofcurvature must necessarily vary at some points as one proceeds aroundthe orifice perimeter. This variation in curvature leads to two majorflow phenomena not shared by circular orifices: (1) the axis of theorifice jet rotates by approximately 90 degrees and (2) the orifice jetplume maintains its initial shape and dissipates more slowly in thepresence of cross-channel flow. The underlying physical reason whynon-circular orifices behave in this manner is because regions ofrelatively small radius of curvature (e.g., rounded vertices oftriangles or ends of elongated slots) undergo net mass flow into the jetplume whereas regions of large radius of curvature (e.g., straight ornearly straight sides) undergo a net outflow from the jet plume. Basedon numerous computational fluid dynamic simulations, the following ruleshave been established:

-   -   1. Jet plumes associated with non-opposing circular orifices        transform into a bifurcated plume or butterfly shape (see FIG.        18).    -   2. Jet plumes associated with slot and triangular jets bow-out        along their straight edges and rotate by approximately 90        degrees (see FIG. 18).        With an appropriate understanding of the flow physics of        non-circular orifices, it is therefore possible to design a        mixing flow pattern for a non-opposing orifice design that will        more effectively deliver the first reactant fluid across the        entire channel gap for a cross-flowing second fluid in a mixing        channel. An example where this is useful is in applications        where good mixing is required but active heat transfer in the        orifice region on the opposite wall is also necessary. Because        circular jets diffuse much more easily for the same flow        conditions, it may not be possible to effectively mix throughout        the entire mixing channel cross-section within a short mixing        length without the use of non-circular orifices. Furthermore, as        illustrated in FIG. 18 and specifically described in Table 1, it        is possible to select the proper order of orifice geometry that        will lead to fluid advection and diffusion patterns that        complement one-another and offer the most homogeneous        distribution of injected fluid into the mixing channel.        Flow Control for Superior Mixing Through Orifices into a        Microchannel

One purpose of in-situ micro-channel mixing is to uniformly mix two ormore separate streams. This process is intended to combine individualstreams of different chemical composition or to bring more than onestream with different thermo-physical characteristics (such astemperature) and mix the streams to give one homogeneous fluidcharacterization.

A flow parameter used in assessing the efficacy of a mixing orificedesign is the momentum vector of a fluid. The momentum vector is definedas follows:

{right arrow over (p)}=½m{right arrow over (u)}|{right arrow over (u)}|

where{right arrow over (p)}=momentum vectorm=mass of moving object{right arrow over (u)}=object velocity vector|{right arrow over (u)}|=object velocity magnitudeGenerally we are dealing with a continuous fluid rather than a discreteobject with mass m. Furthermore, we are most interested in the componentof the momentum vector normal to the cross-sectional area of an orificeor channel. Therefore, it is more appropriate to characterize themomentum of a fluid stream through any orifice or channel by way of themomentum flux given by the following expression:

$\frac{1}{2A}{\int{\int_{A}{\rho \; u^{2}\ {A^{\prime}}}}}$

whereA=cross-sectional area normal to the direction of flowA′=cross-sectional area variable of integrationu=velocity magnitude in the cross-sectional area normal to direction offlowρ=fluid densityThe primary objective of in-situ mixing from a fluidics standpoint is tosupply the appropriate type of momentum source to force the individualstreams to co-mingle and overcome any mass transfer resistance tocombination of the streams. Too small of a momentum source will notovercome mass transfer limitations associated with the relatively slowprocess of molecular diffusion. Too great a momentum source willover-drive the flow, which effectively results in the individual flowstreams remaining largely separated in composition and/orthermo-physical properties.

The efficacy of the mixing process is primarily determined by (1) theratio of the momentum flux of each orifice compared to the cumulativechannel flow momentum flux and (2) the spatial orientation andseparation of the orifices relative to one-another. The momentum of themixing stream is a function of local flow rate as well as geometry andsize of the orifices and channel. The flow stream configurations andorifice geometries are described in the section on classes ofgeometries.

The momentum flux ratio, J, is defined by the following equation:

$J = \frac{\frac{1}{2A_{o}}{\int{\int_{A_{J}}{\rho_{o}u_{o}^{2}\ {A}}}}}{\frac{1}{2A_{C}}{\int{\int_{A_{C}}{\rho_{c}u_{c}^{2}\ {A}}}}}$

whereA_(o)=orifice cross-sectional areaA_(c)=channel cross-sectional areau_(o)=local orifice flow velocity magnitudeu_(c)=local channel flow velocity magnitude just upstream of the orificeρ_(o)=orifice local fluid densityρ_(c)=channel local fluid density

The momentum flux ratio serves as a dimensionless metric for assessingthe performance of an orifice to introduce and mix a stream into achannel. Whereas the local flow patterns themselves may be quite complexand the size and geometries of the orifices vary significantly within amicro-channel application, the momentum flux ratio serves as arelatively simple means of determining how effective an orifice will befor mixing. The momentum flux ratio can either be predicted from a firstprinciples flow simulation or measured experimentally by taking theratio of the area-weighted-average of dynamic pressure in the orifice tothe area-weighted-average of the dynamic pressure in the channelimmediately upstream of the orifice. Dynamic pressure is equal to thetotal local pressure minus the local static pressure.

The injection of fluid into a cross-flowing stream makes it possible toaugment the diffusion mixing process that operates on a relatively longtime scale with a momentum-driven convective mixing process operating ona much shorter time scale. Adjusting the relative contribution of theinjection fluid momentum flux to the cross-flowing channel momentum fluxmakes it possible to balance these momentum drivers and achieve goodmixing. The fluid injection process, both for one-sided orifices andopposing orifices, allows one to more efficiently achieve good mixingwithin a shorter mixing region. At lower values of momentum flux ratios,the orifice jet turns downstream more rapidly than for higher values ofmomentum flux ratio. On the other hand, high momentum flux ratios areassociated with orifice jet plumes that undergo less turning downstreamas it passes through the channel cross-flow. When the cross-flow channelfluid has a density significantly greater than that of the injectionfluid, it is necessary to impart more force to the injection fluid topenetrate and mix with the channel flow. Conversely, when the injectionfluid density is greater than that of the channel cross-flow, lessmomentum should be imparted so that good mixing is obtained. Themomentum flux ratio takes both the relative velocity and density of themixing streams into account to provide a means of evaluating goodmixing. For good mixing to take place between streams, the momentum fluxratio is preferably in the range of between 10 and 400, more preferablybetween 40 and 200 and most preferably between 60 and 155. Note thatthese preferred ranges are equally valid for all gases or liquid.

In terms of spacing of the orifices, if the orifices are arranged on anequilateral triangular pitch array, then the preferredtangent-to-tangent spacing between jets is 6.7D_(H) to 10.2 D_(H) whereD_(H) is the hydraulic diameter of the orifice given by the expression

$D_{H} = {4\; \frac{A}{P}}$

where A and P represent the cross-sectional area and outer perimeter ofthe orifice, respectively. If the orifices are arranged on a squarerectangular pitch array, then the preferred spacing tangent-to-tangentfrom jet to jet is 5.7D_(H) to 8.6 D_(H). The hydraulic diameter isdetermined from the jet dimensions and can be appropriately adjusted togive momentum flux ratios in the ranges described above.

Mixing Example

One embodiment of the invention is the example of opposing jets in amixing manifold configuration. The following example is based on a testdevice actually fabricated and run in the laboratory. Flow enters fromchannels 121 and 122 as illustrated in FIG. 13. The flow from channel122 separates into two streams to fill plenums 123 and 124. Flow is thenmetered through two sets of five opposing jets (125) configured in anequilateral triangular pitch array as illustrated in FIG. 19. The jetplumes from the opposing jet orifices impinge and enhance mixing inchannel 126.

Plenums 123 and 124 should be sized such that flow distribution into theindividual jet ports is uniform. This requires that the width (127) toheight (128) ratio of the plenum in FIG. 13 be within the range of 1:1to 3:1. This example used a width to height ratio of approximately 2:1.The jet orifice diameter and relative spacing will depend upon themixing channel gap height, width, and the relative flow rates andproperties of the two streams in channels 121 and 122. This dependenceis described in the prior section of this patent. For this example, thelocation of the centers of the set of five jet orifices for a 0.040-inchwide mixing channel (one set for each plenum) is given in FIG. 19.

A sample application of this example is mixing of ethylene and aceticacid with an oxygen stream. The relevant flow parameters are given inTable 2. The ethylene and acetic acid component flows through channel121 in FIG. 13 as a pre-mixed feed. Oxygen flows through channel 122,enters plenums 123 and 124, and finally passes through the jet ports 125to mix with the hydrocarbon stream in channel 126.

The target molar ratios for each of the three individual components inthe mixing stream are given as total flow molar ratio in TABLE 2.

TABLE 2 Inlet Flow Conditions for Mixing Example. Chemical SpeciesEthylene Acetic Acid Oxygen Inlet 128 128 128 Pressure (PSIA) Inlet 160160 160 Temperature (° C.) Inlet Flow 36.0 18.0 6.0 Rate (SCCM) TotalFlow 0.6 0.3 0.1 Mole FractionA detailed multi-species computational fluid dynamics calculation of themixing of the two streams was performed using the data from Table 2 asboundary conditions for the calculations. The mole fraction distributionof each constituent species was obtained at three separation locations:2 inches (5.1 cm), 2.5 inches (6.4 cm), and 3-inches (7.6 cm) downstreamin the midplane of the mixing channel. Results from these calculations(see Table 3) show that the cross-sectional distribution of molefraction across the width of the channel is uniform and deviates fromthe target mixing fraction by less than 2% within 2 inches (5.1 cm)downstream of the last two jets. Less than 2% variability in channelcross-sectional chemical species composition is considered near idealand a variability of less than 5% is considered to be adequate for goodmixing. In preferred methods of the invention, adequate mixing isachieved, in more preferred embodiments, the mixing is near ideal; thesemixing qualities can occur, for example, before entering a reactionzone, or before exiting a microchannel.

TABLE 3 Mixing Results for Opposing Jets Example (downstream positionsmeasured relative to the centers of the last two jets in the bulk flowdirection). 2-inches Downstream 2.5-inches Downstream 3-inchesDownstream C2H4 CH3COOH O2 C2H4 CH3COOH O2 C2H4 CH3COOH O2 Minimum MoleFrac 0.6020 0.2916 0.0970 0.6031 0.2925 0.0992 0.6037 0.2930 0.1005Maximum Mole Frac 0.6073 0.2957 0.1065 0.6061 0.2947 0.1044 0.60540.2942 0.1033 Average Mole Frac 0.6045 0.2936 0.1018 0.6045 0.29360.1019 0.6044 0.2936 0.1020

1-63. (canceled)
 64. Microchannel apparatus, comprising a microchannelhaving a cross-sectional area and a central axis (defined by a linethrough the center of the microchannel's cross-sectional area) thatextends in a first direction; a first channel having a central axis(defined by a line through center of the first channel's cross-sectionalarea) that extends in a second direction; wherein the second directionis at an angle of 45° to 135° relative to the first direction; whereinthe microchannel is defined by at least one channel wall and the channelwall has at least one orifice; wherein a portion of the first channel isadjacent to the microchannel; wherein, at a point where the firstchannel is adjacent to the microchannel, the at least one orificeconnects the microchannel with the first channel; and a second channelhaving a central axis (defined by line through center of cross-sectionalarea) that extends in a third direction; wherein the third direction isat an angle of 45° to 135° relative to the first direction; wherein aportion of the second channel is adjacent to the microchannel.
 65. Asystem that mixes fluids in a microchannel, comprising: a first fluidflowing in a microchannel; a second fluid flowing in a direction in aconduit that is adjacent to the microchannel; wherein the second fluidis flowing into the conduit with a momentum number of 0.05 or greater;wherein the second fluid flows into the first fluid in the microchannelthrough at least two orifices that connect the conduit and microchannel;wherein the at least two orifices comprise a first orifice and a secondorifice and wherein the second orifice is further in said direction thanthe first orifice; wherein the first orifice comprises a firstcross-sectional area and the second orifice comprises a secondcross-sectional area; and wherein the second cross-sectional area issmaller than the first cross-sectional area.
 66. The system of claim 65wherein said first cross-sectional area of the first orifice is adjacentto the conduit; wherein said second cross-sectional area of the secondorifice is adjacent to the conduit; wherein the first orifice comprisesa third cross-sectional area that is adjacent to the microchannel;wherein the second orifice comprises a fourth cross-sectional area thatis adjacent to the microchannel; and wherein the third and fourthcross-sectional areas are substantially the same.
 67. The system ofclaim 65 wherein the orifices are not tortuous. 68-74. (canceled) 75.Microchannel apparatus comprising: a microchannel having a hydraulicdiameter and a cross-sectional area, and having a central axis (definedby a line through center of the microchannel's cross-sectional area)that extends in a first direction; a first channel having a central axis(defined by a line through center of the first channel's cross-sectionalarea) that extends in a second direction; wherein the second directionis at an angle of 45° to 135° relative to the first direction; whereinthe microchannel is defined by at least one channel wall and the channelwall has at least one orifice; wherein a portion of the first channel isadjacent to the microchannel; wherein, at a point where the firstchannel is adjacent to the microchannel, the at least one orificeconnects the microchannel with the first channel; wherein the at leastone orifice has a hydraulic diameter, and wherein the ratio of themicrochannel hydraulic diameter to the orifice hydraulic diameter isbetween 2 and
 15. 76. The microchannel apparatus of claim 75 wherein thesecond direction is at an angle of 0° to 135° relative to the firstdirection
 77. The system of claim 65 wherein the microchannel has ahydraulic diameter, and wherein the at least two orifices have hydraulicdiameters, and wherein the ratio of the microchannel hydraulic diameterto hydraulic diameter of each of said at least two orifices is between 2and
 15. 78. The microchannel apparatus of claim 64 wherein themicrochannel has a hydraulic diameter, and wherein the at least oneorifice has a hydraulic diameter, and wherein the ratio of themicrochannel hydraulic diameter to the orifice hydraulic diameter isbetween 2 and
 15. 79. The system of claim 65 wherein the microchannelhas a hydraulic diameter, and wherein the at least one orifice has ahydraulic diameter, and wherein the ratio of the microchannel hydraulicdiameter to the orifice hydraulic diameter is between 2.5 and 4.5.